This instructable describes the installation of a rooftop solar installation, from planning to full connected usage. Contact online >>
This instructable describes the installation of a rooftop solar installation, from planning to full connected usage.
Since you need to connect a grid-tied system to the electric grid, you need permission from the electric utility. You may also need permission from a planning authority. A typical prerequisite is that you have a smart meter - one that is capable of running backwards. So the first place to start is the website of your electric utility, to discover what the procedure is.
My utility does not allow householders to generate significantly more power on an annual basis than they use, so I had to document my expected usage from all loads (heating, cooling, electric vehicle charging, lighting etc.). They also require details of the grid-tie equipment (manufacturer and model numbers, with appropriate certification). So the steps were:
To state the obvious, a solar panel installation needs sunlight. Direct sunlight. You need locations where panels will have an unobstructed view of the sun for at least some of the day.There are various online calculators that will tell you how much sunlight a system will receive in different places in the world, based on past weather averages and on spherical geometry - geographic latitude and calculated sun positions.The one I use is PVWatts Calculator
That assumes your view of the sky is completely unobstructed by trees, other buildings, chimneys, mountains etc. If you do have obstructions, you will need to de-rate the power calculated and install more panels to meet your annual power target. Panels are very susceptible to even partial shading - they are constructed of a large number (maybe 60) of cells in series, and if just one is shaded its electrical resistance will rise and the entire panel will be essentially non-functional. So it''s important not to have a panel partly shaded by something like a chimney or awning. A narrow shadow of something like a chimney bracket is not critical provided it only covers a small bit of any cells.
Typically, the panels are mounted on metal rails, the rails are mounted on brackets, the brackets are fastened to the roof. There are different bracket designs for different roof materials. Since the panels have an expected lifetime of some 30 years, and represent considerable investment in time to install, it is prudent to install them on a roof with a commensurate lifetime, rather than one which will only last another 5 or 10 years. It is possible to remove and re-install panels, but you should consider replacing the roof first, for instance replace tar-paper or wooden shingles with metal or ceramic tile.
Local regulations may require the use of fall-arrest equipment when working on a roof.
Regardless of regulations, metal roofs are very slippery, particularly when sitting or kneeling, and I have some sections with a 1:1 slope. It''s impossible to work without a harness. I have rock-climbing equipment including Jumar ascenders that let me stop at any place on the roof and place my full weight on the harness, with hands free. On my first house I used a belay device with a knot, but the Jumar was much easier. On the first roof, I set an eyebolt in the joist in a pony wall, and passed the rope across the ridge to work on the other side. On my second house, I tied the rope to the snow rail. Since I installed panels on both sides, I had two ropes, one in each direction.
Tools and other items can slide off a roof very easily. They might hit someone underneath, but apart from that it''s just annoying having to retrieve them. Sometimes I secured tools with a lanyard, or stored them in a box that would not slide. Once you have some rails up, you can rest boxes against them.
Power cords and safety lines are a trip hazard. One time I stepped on a loose rope on the metal roof; it was like stepping on a bar of soap. I fell and hit my head; the harness stopped me sliding off the roof but my elbow hurt for months.
Solar panels generate voltage when in sunlight (somewhat obviously). However, the pre-attached connectors have shrouds so that there is little risk of touching the conductors. To stop a panel from being energized, you can cover it with a sheet of cardboard or rubber mat.
You need to decide how many panels are going go on what roof sections, which is going to affect how many microinverters are required, and what electrical connections are needed, as well as how many rails and brackets.
The rail system is designed to have panels fitted side-by-side, separated by a clamp. So the length of rail is the width of one panel plus the width of one clamp, multiplied by the number of panels, plus one more clamp width, plus some margin at the ends. Rails can be extended with a joining piece. You need some space around the edges to safely gain access to work - a couple of feet maybe. If there are vent pipes or chimneys you need to avoid those, leave a space in the grid for instance. Brackets are usually fitted to roof trusses, which are vertical. Rails are placed horizontally across the brackets, and panels vertically across two rails. This arrangement gives most flexibility in where panels may be positioned.
Roof orientation is not especially important, except that in the Northern hemisphere a North-facing roof will not see much sun. With grid-tie, it is the cumulative annual energy that is important, not the instantaneous power. If your roof faces east, you will get more power in the morning but less in the afternoon. If it has a steeper pitch, you will get more power in winter but less in summer. The dominant effect is that the panel produces little power if the sun drops below its horizon. I have panels facing east, south and west on pitches of 1:3 and 1:1, and they all generate power; see graph.
If you are working from architectural plans, do not forget to allow for foreshortening of the panels due to the pitch of the roof. My panels are 65 inches long on a 1:1 pitch roof, but on a floorplan they will appear only 46 inches long. The two PDF drawings show panels and rails on a floorplan, and panels at real aspect ratio on a distorted floorplan.
My first house had a "duroid" tar/paper roof with composite shingles. The brackets are secured with lag bolts into the roof trusses, then covered with a metal shield which slides under the shingle to deflect rainwater. In order to locate the trusses, since I had access to the attic space, I drilled pilot holes either side of the truss from underneath, then drilled a hole from above between them to take the lag bolt. I then sealed the pilot holes, though they were protected by the shield.
Since the microinverters are mounted underneath the panels, they need to be fastened to the rails before the panels are placed. Using the previously worked-out layout, bolt the inverters to the rails with the supplied captive bolts. Mine had washers with oxide-piercing sharps, designed to make a good ground connection between the inverter body and the aluminium rails. There are similar sharps on the panel clamps, to make a connection to the panel frames. Since the inverter connectors are only waterproof when assembled, I placed plastic bags over the inverters in case of rain.
Connect the 240V daisy-chain cable to the inverters and secure with cable ties. Also run a grounding wire to the rails. My kit included grounding lugs with sharps for the purpose.
Industry-standard panels are a convenient size for one person to lift and carry, but not up a ladder in one hand. For my first roof, I used G-clamps to hoist the panels with a rope. Later, I drilled a hole at one end of each panel frame and attached a temporary lifting bolt and lug, with a carabiner secured to a rope. I was able to lean a panel against the side of the house, then drop a rope down from the roof and secure it, then lift the panel straight up and lower it onto the rails.
On the steep pitched roof, I used a pulley block at the apex, which made it easier to adjust the position of the panel. On the shallow pitches, the panels are more-or-less held by friction and the rope is just a precaution.
When wiring the microinverters, keep a note of which panels connect to which inputs of which microinverters - the serial numbers are required for monitoring.
I commissioned groups of panels using an extension cord, to make sure they were all operating properly. The older microinverters used a monitoring system with an ethernet connection, that allowed monitoring with a laptop. The newer ones use a different incompatible monitor using WiFi and a cellphone application. In both cases, it''s possible to see the power produced by each panel.
The daisy-chain cables just plug in to the inverters, but the end of the chain must be wired to the house electrical system. Make sure you fully understand the connection - the inverter cables may not use the colour conventions of your jurisdiction. My older inverters had a 3-conductor cable for North American split-phase 240V, two live conductors and a neutral, with ground provided separately. My newer ones also had a 3-conductor cable, but with two live conductors and a ground. External ground is still required to the rails in either case. For commissioning, I temporarily connected a 3-conductor cable to a 240V outlet, changing the connection for the different inverters.
The inverters take some time to boot up and to characterize the AC supply in order to match it properly. If you don''t see power coming from the panels as soon as you plug them in, wait a while.
My electrical code requires wire connections to be made in a waterproof electrical box. I have regular house wiring with 1-strand conductors coming into the box through the wall, and water-tight inlets for the multi-strand daisy-chain cable. In one place, I had to extend the daisy-chain cable under the panels with flexible cabtire, using crimp connectors and water-tight heatshrink insulation.
Each group of inverters goes to a separate electrical box and then via separate cables to separate ganged pairs of 20A breakers in the breaker panel. There are three boxes on one set of roofs (shown) and two on another.
The monitoring systems track the cumulative energy over time, per day, week or month, and also show instantaneous power for each panel. I wrote some software to collect the instantaneous power figures at regular intervals, easy enough on the old ethernet-connected monitor but somewhat complicated on the newer one.
The graphs show average panel power during a day from three different roof pitches, a shallow pitched garage facing southwest, a shallow pitch facing south, and a steep pitch facing west. The garage starts to get shaded by trees in the afternoon.
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